zlib: fix cygwin build

pkgs/development/libraries/zlib/default.nix

@@ -43,12 +43,17 @@ stdenv.mkDerivation (finalAttrs: {
       hash = "sha256-mpOyt9/ax3zrpaVYpYDnRmfdb+3kWFuR7vtg8Dty3yM=";
     };
 
-  postPatch = lib.optionalString stdenv.hostPlatform.isDarwin ''
-    substituteInPlace configure \
-      --replace '/usr/bin/libtool' '${stdenv.cc.targetPrefix}ar' \
-      --replace 'AR="libtool"' 'AR="${stdenv.cc.targetPrefix}ar"' \
-      --replace 'ARFLAGS="-o"' 'ARFLAGS="-r"'
-  '';
+  postPatch =
+    lib.optionalString stdenv.hostPlatform.isDarwin ''
+      substituteInPlace configure \
+        --replace '/usr/bin/libtool' '${stdenv.cc.targetPrefix}ar' \
+        --replace 'AR="libtool"' 'AR="${stdenv.cc.targetPrefix}ar"' \
+        --replace 'ARFLAGS="-o"' 'ARFLAGS="-r"'
+    ''
+    + lib.optionalString stdenv.hostPlatform.isCygwin ''
+      substituteInPlace win32/zlib.def \
+        --replace-fail 'gzopen_w' ""
+    '';
 
   strictDeps = true;
   outputs = [
@@ -59,7 +64,7 @@ stdenv.mkDerivation (finalAttrs: {
   setOutputFlags = false;
   outputDoc = "dev"; # single tiny man3 page
 
-  dontConfigure = stdenv.hostPlatform.isMinGW;
+  dontConfigure = (stdenv.hostPlatform.isMinGW || stdenv.hostPlatform.isCygwin);
 
   preConfigure = lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
     export CHOST=${stdenv.hostPlatform.config}
@@ -112,7 +117,9 @@ stdenv.mkDerivation (finalAttrs: {
     lib.optionalAttrs (!stdenv.hostPlatform.isDarwin) {
       # As zlib takes part in the stdenv building, we don't want references
       # to the bootstrap-tools libgcc (as uses to happen on arm/mips)
-      NIX_CFLAGS_COMPILE = "-static-libgcc";
+      NIX_CFLAGS_COMPILE = toString (
+        [ "-static-libgcc" ] ++ lib.optional stdenv.hostPlatform.isCygwin "-DHAVE_UNISTD_H"
+      );
     }
     // lib.optionalAttrs (stdenv.hostPlatform.linker == "lld") {
       # lld 16 enables --no-undefined-version by default
@@ -126,7 +133,7 @@ stdenv.mkDerivation (finalAttrs: {
   dontStrip = stdenv.hostPlatform != stdenv.buildPlatform && static;
   configurePlatforms = [ ];
 
-  installFlags = lib.optionals stdenv.hostPlatform.isMinGW [
+  installFlags = lib.optionals (stdenv.hostPlatform.isMinGW || stdenv.hostPlatform.isCygwin) [
     "BINARY_PATH=$(out)/bin"
     "INCLUDE_PATH=$(dev)/include"
     "LIBRARY_PATH=$(out)/lib"
@@ -138,10 +145,14 @@ stdenv.mkDerivation (finalAttrs: {
   makeFlags = [
     "PREFIX=${stdenv.cc.targetPrefix}"
   ]
-  ++ lib.optionals stdenv.hostPlatform.isMinGW [
+  ++ lib.optionals (stdenv.hostPlatform.isMinGW || stdenv.hostPlatform.isCygwin) [
     "-f"
     "win32/Makefile.gcc"
   ]
+  ++ lib.optionals stdenv.hostPlatform.isCygwin [
+    "SHAREDLIB=cygz.dll"
+    "IMPLIB=libz.dll.a"
+  ]
   ++ lib.optionals shared [
     # Note that as of writing (zlib 1.2.11), this flag only has an effect
     # for Windows as it is specific to `win32/Makefile.gcc`.